The yearly elf mass ambush turned up, uncovered by a dog chained near the southwest corner of the map. Once the civilians had been recalled, I checked the path of the elven forces and saw they were near the caged hydra (I have a fair number of cage traps, so there's usually something interesting to unleash on invaders). I'd gotten underwhelming results from caged giants and ettins in the past*, so I was figuring Sulud Couragecontest the Gnarled Mange would mostly sow confusion before being taken down.
Final scores:
Elves: 1 dog (chained)
Sulud: 51 elves, 7 war leopards, 5 war grizzlies, 5 war jaguars, 1 two-humped camel, apparently no lasting wounds; she obligingly was recaptured in a cage trap after the mayhem to await further adventures
Dwarves: 1 panicked war jaguar that strayed in range of a marksdwarf tower; they have also acquired 8 elven prisoners-of-war from the cage traps surrounding the chained dog and a fresh (possibly) supply of loincloths (they can't make 'em, but they sure are happy to wear 'em)
Collateral damage: 1 visiting human axeman who insisted on standing next to the closed entrance bridge, and possibly a psychotic treasure-hunting swordsdwarf who decloaked shortly after cleanup began, shouted something about no one keeping him from a named bronze short sword, turned hostile, and met a steel short sword for his troubles (I'da given him the stupid sword if he'd asked for it; it wasn't even ours, but showed up in the loot after a previous attack)
Lessons learned:
*Hydras like to bite off heads;
*Standard elven military equipment and tactics are useless against hydras;
*Elves are either very courageous or very stupid: even when the utter futility of the attack became obvious, they didn't cut and run
I can't wait to see what the caged bronze colossus does to the next goblin invasion.
*Turns out if the cages are next to each other and you release them at the same time, different kinds of semi-megabeasts attack each other first instead of the approaching goblins